This invention relates generally to intraocular lenses to be implanted within a natural capsular bag in the human eye formed by evacuation of the crystalline matrix from the natural lens of the eye through a anterior capsulotomy in the lens. The invention relates more particularly to novel accommodating intraocular lenses of this kind having a number of improved features including, most importantly, increased amplitude or diopters of accommodation.
The human eye has an anterior chamber between the cornea and iris, a posterior chamber behind the iris containing a crystalline lens, a vitreous chamber behind the lens containing vitreous humor, and a retina at the rear of the vitreous chamber. The crystalline lens of a normal human eye has a lens capsule attached about its periphery to the ciliary muscle of the eye by zonules and containing a crystalline lens matrix. This lens capsule has elastic optically clear anterior and posterior membrane-like walls commonly referred to by ophthalmologists as anterior and posterior capsules, respectively. Between the iris and the ciliary muscle is an annular crevice-like space called the ciliary sulcus.
The human eye possesses natural accommodation capability. Natural accommodation capability involves relaxation and contraction of the ciliary muscle of the eye by the brain to provide the eye with near and distant vision. This ciliary muscle action is automatic and shapes the natural crystalline lens to the appropriate optical configuration for focusing on-the retina the light rays entering the eye from the scene being viewed.
The human eye is subject to a variety of disorders which degrade or totally destroy the ability of the eye to function properly. One of the more common of these disorders involves progressive clouding of the natural crystalline lens matrix resulting in the formation of what is referred to as a cataract. It is now common practice to cure a cataract by surgically removing the cataractous human crystalline lens and implanting an artificial intraocular lens in the eye to replace the natural lens. The prior art is replete with a vast assortment of intraocular lenses for this purpose.
Intraocular lenses differ widely in their physical appearance and arrangement. This invention is concerned with intraocular lenses of the kind having a central optical region or optic and haptics which extend outward from the optic and engage the interior of the eye in such a way as to support the optic on the axis of the eye.
Up until the late 1980s, cataracts were surgically removed by either intracapsular extraction involving removal of the entire human lens including both its outer lens capsule and its inner crystalline lens matrix, or by extracapsular extraction involving removal of the anterior capsule of the lens and the inner crystalline lens matrix but leaving intact the posterior capsule of the lens. Such intracapsular and extracapsular procedures are prone to certain post-operative complications which introduce undesirable risks into their utilization. Among the most serious of these complications are opacification of the posterior capsule following extracapsular lens extraction, intraocular lens decentration, cystoid macular edema, retinal detachment, and astigmatism.
An improved surgical procedure called anterior capsulotomy was developed to alleviate the above and other post-operative complications and risks involved in intracapsular and extracapsular cataract extraction. Simply stated, anterior capsulotomy involves forming an opening in the anterior capsule of the natural lens, leaving intact within the eye a capsular bag having an elastic posterior capsule, an anterior capsular remnant or rim about the anterior capsule opening, and an annular crevice, referred to herein as a cul-de-sac, between the anterior capsule remnant and the outer circumference of the posterior capsule. This capsular bag remains attached about its periphery to the surrounding ciliary muscle of the eye by the zonules of the eye. The cataractous natural lens matrix is extracted from the capsular bag through the anterior capsule opening by phacoemulsification and aspiration or in some other way after which an intraocular lens is implanted within the bag through the opening.
A relatively recent and improved form of anterior capsulotomy known as capsulorhexis is essentially a continuous tear circular or round capsulotomy. A capsulorhexis is performed by tearing the anterior capsule of the natural lens capsule along a generally circular tear line substantially coaxial with the lens axis and removing the generally circular portion of the anterior capsule surrounded by the tear line. A continuous tear circular capsulotomy or capsulorhexis, if performed properly provides a generally circular opening through the anterior capsule of the natural lens capsule substantially coaxial with the axis of the eye and surrounded circumferentially by a continuous annular remnant or rim of the anterior capsule having a relatively smooth and continuous inner edge bounding the opening. When performing a continuous tear circular capsulorhexis, however, the anterior rim may sometimes be accidentally torn, nicked, or otherwise ruptured, which renders the rim prone to tearing when the rim is stressed, as it is during fibrosis as discussed below.
Another anterior capsulotomy procedure, referred to as an envelope capsulotomy, involves cutting a horizontal incision in the anterior capsule of the natural lens capsule, then cutting two vertical incisions in the anterior capsule intersecting and rising from the horizontal incision, and finally tearing the anterior capsule along a tear line having an upper upwardly arching portion which starts at the upper extremity of the vertical incision and continues in a downward vertical portion parallel to the vertical incision which extends downwardly and then across the second vertical incision. This procedure produces a generally archway-shaped anterior capsule opening centered on the axis of the eye. The opening is bounded at its bottom by the horizontal incision, at one vertical side by the vertical incision, at its opposite vertical side by the second vertical incision of the anterior capsule, and at its upper side by the upper arching portion of the capsule tear. The vertical incision and the adjacent end of the horizontal incision form a flexible flap at one side of the opening. The vertical tear edge and the adjacent end of the horizontal incision form a second flap at the opposite side of the opening.
A third capsulotomy procedure, referred to as a beer can or can opener capsulotomy, involves piercing the anterior capsule of the natural lens at a multiplicity of positions along a circular line substantially coaxial with the axis of the eye and then removing the generally circular portion of the capsule circumferentially surrounded by the line. This procedure produces a generally circular anterior capsule opening substantially coaxial with the axis of the eye and bounded circumferentially by an annular remnant or rim of the anterior capsule. The inner edge of this rim has a multiplicity of scallops formed by the edges of the pierced holes in the anterior capsule which render the annular remnant or rim prone to tearing radially when the rim is stressed, as it is during fibrosis as discussed below.
Intraocular lenses also differ with respect to their accommodation capability and their placement in the eye. Accommodation is the ability of an intraocular lens to accommodate, that is, to focus the eye for near and distant vision. Certain patents describe alleged accommodating intraocular lenses. Other patents describe non-accommodating intraocular lenses. Most non-accommodating lenses have single focus optics which focus the eye at a certain fixed distance only and require the wearing of eye glasses to change the focus. Other non-accommodating lenses have bifocal optics which image both near and distant objects on the retina of the eye. The brain selects the appropriate image and suppresses the other image, so that a bifocal intraocular lens provides both near vision and distant vision sight without eyeglasses. Bifocal intraocular lenses, however, suffer from the disadvantage that each bifocal image represents only about 40% of the available light, and a remaining 20% of the light is lost in scatter.
There are four possible placements of an intraocular lens within the eye. These are (a) in the anterior chamber, (b) in the posterior chamber, (c) in the capsular bag, and (d) in the vitreous chamber. The intraocular lenses disclosed herein are for placement in the capsular bag.
This invention provides an improved accommodating intraocular lens to be implanted within a capsular bag of a human eye which remains intact within the eye after removal of the crystalline lens matrix from the natural lens of the eye through an anterior capsule opening in the natural lens. This anterior opening is created by performing an anterior capsulotomy, preferably an anterior capsulorhexis, on the natural lens and is circumferentially surrounded by an anterior capsular rim which is the remnant of the anterior capsule of the natural lens. An improved accommodating intraocular lens according to the invention includes a central optic having normally anterior and posterior sides and extended portions spaced circumferentially about and extending generally radially out from the edge of the optic. These extended portions have inner ends joined to the optic and opposite outer ends movable anteriorly and posteriorly relative to the optic. To this end, the extended portions are either pivotally or flexibly hinged at their inner ends to the optic or are resiliently bendable throughout their length. In this disclosure, the terms xe2x80x9cflexxe2x80x9d, xe2x80x9cflexingxe2x80x9d, xe2x80x9cflexiblexe2x80x9d, and the like are used in a broad sense to cover both flexibly hinged and resiliently bendable extended portions. The terms xe2x80x9chingexe2x80x9d, xe2x80x9chingedxe2x80x9d, xe2x80x9chingingxe2x80x9d, and the like are used in a broad sense to cover both pivotally and flexibly hinged extended portions.
The lens is surgically implanted within the evacuated capsular bag of a patient""s eye through the anterior capsule opening in the bag and in a position wherein the lens optic is aligned with the opening, and the outer ends of the lens extended portions are situated within the outer perimeter or cul-de-sac of the bag. The lens has a radial dimension from the outer end of each extended portion to the axis of the lens optic such that when the lens is implanted within the capsular bag, the outer ends of the extended portions engage the inner perimetrical wall of the bag without stretching the bag.
After surgical implantation of the accommodating intraocular lens in the capsular bag of the eye, active endodermal cells on the posterior side of the anterior capsule rim of the bag cause fusion of the rim to the elastic posterior capsule of the bag by fibrosis. This fibrosis occurs about the lens extended portions in such a way that these extended portions are effectively xe2x80x9cshrink-wrappedxe2x80x9d by the fibrous tissue in such a way as to form radial pockets in the fibrous tissue which contain the extended portions with their outer ends positioned within the outer cul-de-sac of the capsular bag. The lens is thereby fixated within the capsular bag with the lens optic aligned with the anterior capsule opening in the bag. The anterior capsule rim shrinks during fibrosis, and this shrinkage combined with shrink-wrapping of the extended portions causes some radial compression of the lens in a manner which tends to move the lens optic relative to the outer ends of the extended portions in one direction or the other along the axis of the optic. The fibrosed, leather-like anterior capsule rim prevents anterior movement of the optic and urges the optic rearwardly during fibrosis. Accordingly, fibrosis induced movement of the optic occurs posteriorly to a distant vision position in which either or both the optic and the inner ends of the extended portions press rearwardly against the elastic posterior capsule of the capsular bag and stretch this posterior capsule rearwardly.
During surgery, the ciliary muscle of the eye is paralyzed with a ciliary muscle relaxant, i.e. a cycloplegic, to place the muscle in its relaxed state. Following surgery, a ciliary muscle relaxant is periodically introduced into the eye throughout a post-operative fibrosis and healing period (from two to three weeks) to maintain the ciliary muscle in its relaxed state until fibrosis is complete. This drug-induced relaxation of the ciliary muscle prevents contraction of the ciliary muscle and immobilizes the capsular bag during fibrosis. By this means, the lens optic is fixed during fibrosis in its distant vision position within the eye relative to the retina wherein the lens presses rearwardly against and thereby posteriorly stretches the elastic posterior capsule of the capsular bag. If the ciliary muscle was not thus maintained in its relaxed state until the completion of fibrosis, the ciliary muscle would undergo essentially normal brain-induced vision accommodation contraction and relaxation during fibrosis. This ciliary muscle action during fibrosis would result in improper formation of the pockets in the fibrosis tissue which contain the extended portions of the lens. Moreover, ciliary muscle contraction during fibrosis would compress the capsular bag and thereby the lens radially in such a way as to very likely dislocate or decenter the lens from its proper position in the bag or fix the optic in the near vision position.
When the cycloplegic effect of the ciliary muscle relaxant wears off after the completion of fibrosis, the ciliary muscle again becomes free to undergo normal brain-induced contraction and relaxation. Normal brain-induced contraction of the muscle then compresses the lens radially, relaxes the anterior capsule rim, and increases vitreous pressure in the vitreous chamber of the eye. This normal contraction of the ciliary muscle effects anterior accommodation movement of the lens optic for near vision by the combined action of the increased vitreous pressure, anterior capsule rim relaxation, and the anterior bias of the stretched posterior capsule. Similarly, brain-induced relaxation of the ciliary muscle reduces vitreous pressure, relieves radial compression of the lens, and stretches the anterior capsule rim to effect posterior movement of the lens optic for distant vision.
Normal brain-induced relaxation and contraction of the ciliary muscle after the completion of fibrosis thus causes anterior and posterior accommodation movement of the lens optic between near and distant vision positions relative to the retina. During this accommodation movement of the optic, the lens extended portions undergo endwise movement within their pockets in the fibrous tissue.
The described lens embodiments of the invention conform to one of the following basic lens configurations: (a) a lens configuration, hereafter referred to as a posteriorly biased lens configuration, in which the hinges of hinged extended portions and the inner ends of resiliently bendable extended portions are located posteriorly of or approximately in a plane (tip plane) normal to the optic axis and containing the outer tips of the extended portions when the lens occupies its posterior distant vision position against the posterior capsule of the eye, and (b) a lens configuration, hereafter referred to as an anteriorly biased lens configuration, in which the hinges of hinged extended portions and the inner ends of resiliently bendable extended portions are located forwardly of the tip plane when the lens occupies its posterior distant vision position against the posterior capsule of the eye. Radial compression of a posteriorly biased lens by constriction of the ciliary muscle during accommodation initially urges the lens optic posteriorly against the more dominant anterior forces of the stretched posterior capsule and the increasing vitreous pressure which combine to move the optic forwardly in accommodation against the rearward bias of the compressing lens until the hinges of hinged extended portions or the inner ends of resiliently bendable extended portions move forwardly of the tip plane. Continued radial compression of the lens by ciliary muscle constriction then aids anterior accommodation movement of the lens. Radial compression of an anteriorly biased lens by constriction of the ciliary muscle urges the lens optic anteriorly and thus aids the dominant anterior forces of the stretched posterior capsule and the increasing vitreous pressure throughout the range of lens accommodation.
According to another important aspect of this invention, the extended portions of a presently preferred lens embodiment are generally T-shaped haptics each including a haptic plate and a pair of relatively slender resiliently flexible fixation fingers at the outer end of the haptic plate. In their normal unstressed state, the two fixation fingers at the outer end of each haptic plate extend laterally outward from opposite edges of the respective haptic plate in the plane of the plate and substantially flush with the radially outer end edge of the plate to form the horizontal xe2x80x9ccrossbarxe2x80x9d of the haptic T-shape. The radially outer end edges of the haptic plates are circularly curved about the central axis of the lens optic to substantially equal radii closely approximating the radius of the interior perimeter of the capsular bag when the ciliary muscle of the eye is relaxed. During implantation of the lens in the bag, the inner perimetrical wall of the bag deflects the haptic fingers generally radially inward from their normal unstressed positions to arcuate bent configurations in which the radially outer edges of the fingers and the curved outer end edges of the respective haptic plates conform approximately to a common circular curvature closely approximating the curvature of the inner perimetrical wall of the bag. The outer T-ends of the haptics then press lightly against the perimetrical bag wall and are fixated within the bag perimeter during fibrosis to accurately center the implanted lens in the bag with the lens optic aligned with the anterior capsule opening in the bag.
The haptic plates of certain described lens embodiments are narrower in width than the optic diameter and are tapered so as to narrow in width toward their outer ends. These relatively narrow plates of the haptics flex or pivot relatively easily to aid the accommodating action of the lens and form haptic pockets of maximum length in the fibrous tissue between the haptic fingers and the optic which maximize the accommodation movement of the lens optic. The tapered haptics, being wider adjacent to the optic, can slide radially in the capsular bag pockets during contraction of the of the ciliary muscle to enable forward movement of the optic for vision accommodation.
In some described lens embodiments of the invention, the lens optic and extended portions are molded or otherwise fabricated as an integral one piece lens structure in which the inner ends of the extended portions are integrally joined to the optic, and the extended portions are either resiliently flexible at each point throughout their length or have flexible hinges at their inner ends adjacent the optic at which the extended portions are hingable anteriorly and posteriorly relative to the optic. In other described lens embodiments, the optic and extended portions are formed separately and have mating hinge portions which interengage to pivotally join the optic and extended portions. In some of these described embodiments, the extended portions are T-shaped haptics formed by molding or otherwise forming the flexible haptic fingers integrally with the haptic plates proper. In other described inventive embodiments, the extended portions are T-shaped haptics having T-shaped reinforcing inserts or inlays which both reinforce the haptic plates and provide the haptics with their T-shapes. Still other described embodiments have reinforcing inserts which reinforce the haptics, provide the haptics with their T-shapes, and/or provide the haptics and optic with mating pivotal hinge portions for pivotally connecting the haptics to the optic.
According to another important aspect, the invention provides an accommodating intraocular lens having haptics which are thickened so as to increase in thickness toward their inner ends and have contoured, convexly rounded posterior surfaces adjacent their inner ends. These contoured haptic surfaces and the posterior surface of the lens optic are disposed relative to one another in the axial direction of the optic axis in such a way that when the intraocular lens occupies its posterior distant vision in the eye with the ciliary muscle relaxed, the lens contacts the posterior capsule of the eye in one of the following ways: (a) only the posterior surfaces of the lens haptics contact the posterior capsule, (b) only the posterior surface of the lens optic contacts the posterior capsule, (c) the posterior surfaces of both the haptics and optic contact the posterior capsule. In lens configurations (a) and (c) above, the contoured posterior surfaces of the haptics slide along the posterior capsule during constriction of the ciliary muscle to increase and enhance anterior accommodating movement of the optic. In lens configuration (a), the posterior surface of the optic is spaced from the posterior capsule to permit laser capsulotomy of the posterior capsule without laser damage to the lens optic in the event that the posterior capsule becomes cloudy after implantation of the lens.
A primary and perhaps the most important aspect of the invention is concerned with increasing the accommodation amplitude of the lens, that is the distance the lens optic moves along the axis of the eye during contraction of the ciliary muscle from its relaxed distant vision state to its contracted near vision state. This amplitude is commonly measured and stated in units which are referred to as diopters of accommodation. The maximum accommodation amplitude or diopters of accommodation which the eye will accommodate varies from patient to patient. Some patient""s eyes, for example, will accommodate on the order of 3.5 diopters of accommodation. Other patient""s eyes will accommodate a maximum of only about 1.75 diopters of accommodation. Accordingly, it is desireable that an accommodating intraocular lens according to this invention be capable of at least 3.5 diopters of accommodation so that it can be used on a patient who can accommodate such a lens and thereby eliminate the need for the patient to wear glasses for near vision.
According to this latter aspect of the invention, the diopters of accommodation of the present accommodating intraocular lens are increased in either or both of the following ways: (a) moving the hinges of lens extended portions or haptics anteriorly relative to the posterior capsule engaging surface(s) of the lens optic in the manner explained earlier so as to increase the portion of ciliary muscle contraction over which the resulting muscular compression of the lens produces an anterior accommodating force on the lens optic, (b) increasing the optical power of the lens, and thereby the amount of vision accommodation produced by any given accommodation movement of the optic, by shaping the optic so that most of its optical power is at the posterior side of the optic and the posterior surface of the optic is steeply curved to retain the optic sharply focused on the retina.
Presently preferred accommodating intraocular lenses of the invention are described. These preferred lenses are anteriorly biased lens including generally T-shaped, flexibly hinged haptics and optics whose posterior portions provide most of the optical power of the optics. These optics cooperate with the anteriorly biased configurations of the lenses to increase accommodation amplitude or diopters of accommodation by both of the ways mentioned above.